Funding is requested for an ImageStreamX-markII (ISX-MKII) imaging flow cytometer to replace a first generation ImageStream-100 cytometer. At the time of its commercial introduction in 2006, the IS-100 uniquely combined flow cytometry with quantitative image analysis. In anticipation of the applicability of this then novel platform or many of our NIH-funded users, the IS100 was acquired. The introduction of the ImageStream technology to our user group has been very successful leading to the award of 3 additional NIH-funded grants that rely heavily on this technology. Based on the success of implementing the IS100 at RPCI, the clear benefit of the technology to our research base and its high usage, an additional ImageStream, the ImageStreamX (ISX) was purchased as a second ImageStream platform with Institute support in 2009 and upgraded to the third generation ISX-MK-II in 2012. In addition, RPCI also invested in the expanded computational and data storage infrastructure and personnel needed in support of the increasing demand for this technology by the RPCI research base. The advanced ImageStream application demands of our user base enabled by the technological advancements implemented in the 3rd generation ISX-MKII have rendered the IS100 obsolete. Thus, the ISX-MK-II currently carries 100% of the work load and is operating at >80% capacity without a functional back up. The purchase of an additional ISX-MKII to replace the now obsolete IS100 will allow our facility to meet the increasing demand for advanced ImageStream applications and provide backup capability when the current machine is out-of-service due to maintenance or repair needs.